During the manufacture of printed wiring boards, the board substrate is placed in a bath containing an etchant fluid for etching away parts of the copper circuit paths located on the surfaces of the substrate which parts have not been covered or coated during a previous step in the manufacturing process. A typical bath contains 500 gallons of etchant fluid and after continuous use the fluid becomes contaminated with copper etched from the dipped substrates. As the etchant fluid becomes more and more contaminated with copper it becomes less effective as an etchant until the fluid becomes spent and is no longer usable.
In another process for the manufacture of printed wiring boards, copper is added to circuit patterns present on the board substrate by dipping the substrate into a bath containing an electroless fluid. Such fluid typically comprises copper sulfate and ammonium hydroxide. Chemical reaction between the substrate circuit patterns and the bath fluid sets up an electric field which moves copper from the bath to the substrate and after being submerged in the bath for a certain period of time the circuit board is removed from the bath. As a final step in the electroless process the circuit board is dipped in a bath of copper ammonium persulfate to remove copper oxide from the surface of the copper circuits on the board and to "brighten up" the copper circuitry. As more and more substrates are processed the electroless and copper ammonium persulfate bath fluids become contaminated such that eventually they become spent.
When the etchant, electroless and copper ammonium persulfate fluids become spent they are pumped from the circuit board manufacturing baths to a processing area to recover copper and copper oxide present in the spent fluids. Present processing methods allow for recovery of only 70 to 75% of the copper and copper oxide in the spent fluids while also leaving ammonia in the finally treated solutions as an unwanted by-product of the process. In order to meet efluent discharge standards the ammonia must be removed from the final solutions prior to discharge of the solutions. Typically this is performed by a second treatment of the solutions to destroy the ammonia and further remove any soluable copper existing in the solutions, which second treatment is labor intensive and costly because of the additional chemicals required. Also, the treatment area requires additional ventilation to remove ammonia gas formed during the second treatment.
There is a need therefore for a process for treating spent etchant, electroless and copper persulfate fluids, or solutions, which increases recovery of the copper and copper oxide present in the spent fluids and which provides a final solution free of ammonia.